The present invention is related generally to the field of internal combustion engines, and more particularly, to the field of engine braking in connection with such internal combustion engines.
On highway trucks often carry heavy loads that can total as much as eighty thousand pounds. These trucks have a significant amount of momentum while travelling down the road, especially when travelling at highway speeds, and often require large brakes associated with the wheels (generally referred to as the service brakes) to slow the truck. The service brakes generally rely on friction to slow the wheels and therefore must convert momentum energy of the truck into heat. Since the service brakes are subject to a significant amount of heat and wear in connection with slowing the vehicle, they can represent a significant operating expense if used inefficiently.
Truck manufacturers and operators have recognized that there is a need to be able to generate braking force through devices other than the service brakes. By using other devices the truck operator can extend the life of the service brakes and therefore decrease the operating cost of the truck. Engine compression brakes are one such way to achieve braking force. In general, engine compression brakes create braking force by allowing air that has entered the engine cylinders during the intake stroke to be compressed during the compression stroke, thereby consuming energy. Then, prior to the expansion stroke of the piston (which would return some of the energy stored in the compressed air back to the piston), the exhaust valve is opened to simply exhaust the compressed air. In this manner the engine acts as a compressor, relieving the compressed air out the exhaust, thereby consuming energy from the wheels through the drivetrain to create a braking force. Although, engine compression braking through the selective use of the cylinder valves works well, it would also be desirable to be able to controllably apply additional engine braking force.
The present invention is directed toward overcoming these and other drawbacks associated with prior art systems.
In one aspect of the present invention, an engine braking system is disclosed for use on an internal combustion engine, having fuel injectors associated with said engine. Also associated with the engine is a pump that provides pressurized fluid to the fuel injectors. An electronic controller is associated with the engine and determines a desired level of engine braking in response to determined engine operating conditions and produces a pump signal as a function of the desired level of engine braking signal.